In the conventional ceiling electric fan, its blowing force may be varied by controlling its speed. Since the fan blades are the fixed type, the blowing scope is constant; therefore, it has the following drawbacks:
(1) When just several persons being present and requiring a smaller blowing scope, the fan still provides a large or constant blowing scope, which would cause energy to be wasted.
(2) When being used for cool or warm air circulation in a room, it will be unable to mix the temperature difference evenly because of the fixed blowing scope and dead angle, as shown in FIG. 1-1.